Blackthorn is a village and civil parish in the Cherwell District of Oxfordshire about southeast of Bicester. The parish is bounded by the River Ray to the south, tributaries of the Ray to the east and north and field boundaries to the west. The parish's eastern boundary also forms part of the county boundary with Buckinghamshire.
The old village lies between the A41 and B4011 main roads. Newer housing on the east side of the neighbouring village of Ambrosden is in fact in the parish of Blackthorn. The 2011 Census recorded a parish population of 317.